Acoustic generators known as stem-jet or Hartmann whistles have been developed which produce a high frequency sonic vibration useful in spray drying and defoaming. Such a device is disclosed in U.S. Pat. No. 2,519,619 issued Aug. 22, 1950 in the name of J. I. Yallott et al in which a high velocity air jet stream impinges on a cavity resonator to produce a high energy vibratory sonic field at the resonator frequency.
This principle has been used to atomize a liquid into a micromist by projecting the liquid into the area of the sonic vibrations. One such generator is disclosed in U.S. Pat. No. 3,081,946 issued Mar. 19, 1963 in the name of R. S. Soloff in which the liquid to be atomized is projected through radial apertures in the body of the generator into the sound field. The problem with such a spray nozzle is that, except at a specific pressure of the liquid at a given volume of delivery, the liquid at the core of the jets issuing from the apertures are not as well atomized as the liquid near the lateral periphery of the jets and consequently larger droplets of liquid are contained in the spray. Consequently optimum operation of the device requires a predetermined constant pressure and rate of delivery of liquid which restricts it to a relatively narrow range of efficiency.
It is an object of the present invention to provide a sonic liquid atomizing device which is operable efficiently over a wider range of pressure of the liquid delivered to the device for atomization.